This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A083998 #7 Sep 01 2021 03:40:42 %S A083998 3,1,1,23,21,3,67,17,3,39,19,33,21,39,77,121,207,9,9,93,53,1,57,93,41, %T A083998 339,9,57,63,1,1091,273,199,83,213,529,569,397,21,71,481,243,111,419, %U A083998 273,231,63,277,483,201,531,77,139,1313,529,1443,587,649,351,273,189 %N A083998 a(1) = 3; then numbers such that the concatenation a(n)a(n-1)...a(2)a(1)a(2)...a(n-1)a(n) is a prime. %Y A083998 Cf. A083996, A083997, A083999, A084000, A083401. %K A083998 base,nonn %O A083998 1,1 %A A083998 _Amarnath Murthy_, May 23 2003 %E A083998 More terms from _Ray Chandler_, Aug 03 2003